The present invention relates to aqueous liquids containing a soluble zinc salt, and more particularly, to so called heavy brines having a density of about 14.2 pounds per gallon (ppg) or greater.
In recent years, the practical operating range of clear brines for use in the oil and gas industry has been significantly extended by utilizing soluble zinc salts, particularly zinc bromide, so that the advantages of clear brines can now be obtained with fluids having densities as high as 19.2 ppg at ambient temperatures and pressures.
The high density clear brines are used extensively: as completion fluids, to minimize plugging of perforation tunnels, to protect formation permeability, and to minimize mechanical problems; as workover fluids, for the same reasons; as packer fluids, to allow easy movement and retrieval of the packer; for underreaming, gravel-pack and sand consolidation applications; as kill fluid or ballast fluid; for wire-line work; and as drilling fluids.
Clear brines having a density of 14.2 ppg or lower are generally formulated to contain sodium chloride, sodium bromide, potassium chloride, calcium chloride, calcium bromide, or mixtures of these salts. Clear brines having a density up to about 15.2 ppg can be formulated with calcium chloride and calcium bromide; however, if the brine must have a low crystallization temperature, then clear brines in this density range are generally formulated to contain a soluble zinc salt. Zinc bromide is preferred because brines containing it are less corrosive than brines containing zinc chloride. Clear brines having a density greater than about 15.2 ppg are formulated to contain zinc bromide.
Viscous clear fluids are sometimes desired. Generally, hydroxyethyl cellulose (HEC) and xantham gum (XC) polymers are compatible with the fluids which do not contain zinc salts. However, at the higher densities, the hydration of the viscosifiers is significantly slower. HEC is generally considered as unsatisfactory for use in fluids containing zinc salts. However, methods of activating HEC, XC polymer, and other water soluble polymers such that they readily hydrate in heavy brines containing zinc bromide have been disclosed in the following co-pending patent applications, incorporated herein by reference for all purposes: Ser. No. 119,805 filed Feb. 8, 1980, now U.S. Pat. No. 4,330,414, for Dispersible Hydrophilic Polymer Compositions; Ser. No. 196,367 filed Oct. 14, 1980, for Dispersible Hydrophilic Polymer Compositions; Ser. No. 146,286 filed May 5, 1980, for Compositions and Method for Thickening Aqueous Brines; and Ser. No. 161,444 filed June 20, 1980, for Thickened Heavy Brines.
It has been found that clear heavy brines containing soluble zinc salts foam upon mixing. In the presence of a hydrophilic polymer viscosifier such as HEC, the foam is stabilized to the extent that an excessive aging time is required to allow the foam to break and be eliminated.